Recovery and recrystallisation in quartz
The large, strongly-strained quartz grain in the centre shows undulose extinction.
Rather than varying smoothly across the grain, however, the extinction reveals a patchwork of
subgrains. These result from the process of recovery, in which dislocations
migrate to form planar arrays separating relatively strain-free domains with a small
angular mismatch. Above and below, quartz has recrystallised into new, smaller
grains. These in turn have begun a second cycle of deformation - their boundaries
are no longer polygonal but interlobate.
Crossed polars. Field of view 1.75 mm.
Moine meta-sandstone Ø500, Scotland